function dragstart_handler(ev) {
    // Add the target element's id to the data transfer object
    ev.dataTransfer.setData("text/plain", ev.target.id);
}
function dragover_handler(ev) {
    ev.preventDefault();
}
function drop_handler(ev) {
    ev.preventDefault();
    // Get the id of the target and add the moved element to the target's DOM
    var data = ev.dataTransfer.getData("text/plain");
    ev.target.appendChild(document.getElementById(data));
}